In order to make the anchor bolt support prestress field fully diffuse in the composite rock stratum, improve the overall bearing capacity of surrounding rock, and give full play to the role of active support of the anchor bolt, a self-made 1:1-scale composite rock stratum similarity simulation test bed was used to compare and analyze the distribution of the anchor bolt support prestress field using different anchoring surrounding rock lithology and anchorage lengths, and the principle for optimum selection of anchoring parameters of composite rock stratum was proposed based on the test results. Considered from the point of view of stress diffusion, the effect of prestress diffusion of end anchorage bolts is better than that of lengthening anchorage; at the same time, the anchorage section should be preferentially arranged in hard rock, and the area of anchorage section near the free section should avoid the structural plane of surrounding rock. In conclusion, an industrial test was carried out under the conditions of a deep composite roof of the 2# coal seam in Qinyuan Mining Area, which determined a reasonable anchoring method and position of the composite roof under different conditions and achieved good results.